The overall goals of this proposal are to generate a series of overlapping cloned DNA fragments from each of human chromosome 21 and human chromosome 22, and to produce high resolution physical maps for both of these autosomes. Cosmid libraries will be constructed in the vector pWE15 using high molecular weight DNA extracted from human X rodent somatic cell hybrid lines containing either human chromsome 21 or 22. Cosmid colonies containing human inserts will be isolated by preferential hybridization to human repetitive sequences, and will be gridded by an automated procedure into 96 member assays. Using the "end labelling" capacity of the pWE15 vector, a series of bidirectional chromosome walks will be initiated from a series of 20 primary cosmids identified by hybridization with probes of known physical and genetic map locations. Overlapping cosmids will be restriction mapped to discover the degree of overlap co check to check for errors and to yield a high resolution physical map of each chromosome. Because the mapped overlapping DNA sequences provided by this proposal would be at hand in a workable vector, this strategy would allow the knowledge gained from the physical map to be immediately applied to a number of areas of the human biology and medicine. Thus, the cloned and mapped sequences can be used to elucidate the mechanism of disordered chromosome segregation in Downs Syndrome, to facilitate cloning of disease genes mapped to these chromosomes (eg: chromosome 21-Familial Alzheimer's Disease; Chromosome 22- Bilateral Acoustic Neurofibromatosis, Metachromatic Leukodystrophy, Di George Syndrome; to clone breakpoints of chromosome translocation associated with disease, as well as to isolate genomic sequences for genes which have not yet been cloned, but which have been mapped to these chromosomes.